Facsimile system and method



Sept. 3, 1946. E. M. DELORAIN E AL 2,406,812

FACSIMILE SYSTEM AND METHOD Filed Jan. 30, 1945 4 Sheets$heet l TRIM/5M1 TTE E INVENTORS EDMOND M. DELORfl/NE HENRI a. BUSIGNIES BY LOU/S n. m-Rasn ATTQEE'VEY Sept. 3, 1946. i E. M. DELORAINE ET AL 2,406,812.

' FACSIMILE SYSTEM AND METHOD Fil ed Jan. so, 1945 4 Sheets-Sheet 2 INVENTORS EDMOND M. 0540mm: HENRI a. BUSIGN/Es LOUIS fl- ROS/9 TORNEY Sep t. 3,1946.

E. M. DELQRAINE ETAL FACSIM ILE SYSTEM AND METHOD Filed Jan. 50, 1945' TRANSMITTING DRUM v ARE BLY 75 HORIZONTRL DEFLECTOR CILLRTOR INVENTORS EDMOND M. DELORfl/N' HENRI G. SUSIE/WES .ATTOIMZEY 4 Sheets-Sheet 3 Sept. 3, 1946. E. M. DELORAINE ET AL FACSIMILE SYSTEM AND METHOD Filed Jan. so, 1943 4 Shecs-Sheet 4 INVENTORS EDMOND M. BELOW/NE HENRI 6. BUSIGN/ES BY tall/5 H. BIRD-SH Patented Sept. 3, 1946 FACSIMILE SYSTEM AND METHOD Edmond M. Deloraine, New York, Henri G. Busignies, Forest Hills, and Louis A. de Rosa, Staten Island, N. Y., assignors to Federal Telephone and Radio Corporation, Newark, N. J., a

corporation of Delaware Application January 30, 1943, Serial No. 474,144

11 Claims. 1

This invention relates to communication systems and more particularly to radio communication systems of the built-up character or simulated facsimile type.

It is often necessary to provide a system in which communication can be maintained despite relatively high level interference. In the time of war, high level interference may be in the form of intentional jamming by enemy stations. At the same time it is quite necessary to maintain communication despite these attempts of the enemy to disrupt the same. As a general rule telegraphic code communications are easier to read through interference than the voice si nals. Telegraphic code signals, however, may be jammed by transmitter stations sending out impulses having substantially a telegraphic code character. 7

It is a principal object of our invention to provide a communication system which will be effective even in the presence of high level interference.

It is a further'object of our invention to provide built-up character systems in which the received signals are rendered effective by visual indicating or recording means.

It is a still further object of our invention to provide a system wherein the signals are transmitted during an interval which is short relative to the spacing therebetween, and are characterized by a steep wavefront and a relatively high peak to average power.

It is a still further object of our invention to provide at the receiver means for eliminating relatively low level interference signals before reproducing the received signals.

In accordance with our invention, we provide a transmitter for transmitting a high level signal composed of a relatively short train of impulses, the impulses each representing a portion of a desired character. At the receiver these signals are translated .and visually reproduced on an oscillograph screen 01' some well known type of recording medium. Preferably, a limiter is provided at the receiver to pass only those portions of the received signal above a predetermined energy level. Since the interference signals are generally lower in amplitude, for the same power expended, the interference is quite largely eliminated by the limiting action at 'the receiver. When a limiter is not provided the interference will generally form only a background for the stronger wanted signals.

A better understanding of our invention and the objects and features thereof may be had 2 from the particular description of a few embodiments thereof made with reference to the accompanying drawings, in which:

Fig. 1 is a diagrammatic View illustrating a possible form of transmitter-receiver equipment;

Fig. 2 is a schematic showing of the transmitting apparatus of Fig. 1 with the cover partly broken away;

Fig. 2A is a detail of the light shutter of the transmitter;

Fig. 3 is a schematic diagram of the transmitter-receiver apparatus explaining operation thereof;

Fig. 4 is a diagram of an embodiment of the receiver scanning circuit;

Fig. 5 is a. set of curves explaining the operation of the circuit of Fig. 4; and

Fig. 6 is a diagram of the oscillograph screen explaining the reproduction of a character.

Turning first to Figs. 1 and 2', I0 represents a casing covering a form of transmitter-receiver apparatus which may be used in accordance with our invention. This housing 10 includes a transmitter portion comprising keyboard ll, knob [2, the purpose of which will be stated later, and a knurled knob 14 which may be used for starting the drive motor for the transmitter equipment when a synchronous motor is used. The transmitter preferably is in the form generally similar to that disclosed in our copending application, Serial No. 469,056, filed December 15, 1942. This arrangement comprises a drum 20, Fig. 2, rotated by some means not shown. On drum 20 are arranged perforations 2| which each represent a series of signal elements forming a particular character to be transmitted. Within drum 20 is provided a photo cell 22 and externally of the drum is provided a light source 23 and reflecting mirror 24 serving to direct the light from 23 generally toward photo cell device 22. The light, however, is prevented from impinging on cell 22 by reason of shutters 25 controlled by selectively operated keys 26. Preferably, drum 20 is maintained continuously in rotation at a speed several times higher than the normal operating cadence of the keys 26. Thus, upon depression of any selected key 26 the drum will rotate a plurality of times. The shutter arrangement is designed to permit transmission of only one character even though the drum is brought into transmitting position a plurality of times for each key depressed. This single transmission is timed to start at the beginning of the selected character.

The shutter operation may be better understood by reference to Fig. 2A. Support plate A is provided with a light passing opening 2 !A. A cam with a raised portion 22A is arranged for rotation with the drum 28. The movable shutter plate 23A is provided with a light passing opening 24A and a lug portion 25A, and is held in place normally by untensioned spring 28A. Upon depression of a key, pull bar 26A pulls shutter plate 23A to the right tensioning spring 28A until pull bar cam 21A is positioned above the releasing cam. Rotation of the cam causes projection 22A to raise pull bar 26A releasing shutter plate 23A when the proper drum position is reached. Spring 25A upon release pulls plate 23A to the left and the momentum of the shutter 23A is sufficient to cause opening 24A to register with 2|A permitting passage of light and at the same time momentarily slightly compressing spring 28A, which upon its return will again put the openings out of alignment. The characteristics of the spring 28A and the weight and friction of shutter plate 23A are proportioned to provide only one opening of the shutter for a single key operation. Upon release of the key, draw bar 26A returns to engagement with lug 25A on shutter plate 23A under control of a key return means, not shown.

In order that only one key may be depressed at one time, we provide any known form of blocking mechanism which may prevent depression of any otherkey while one is in the depressed position. This mechanism may, as is well known in the art, comprise a row of balls of such dimension that depression of one key pushes the balls together so that no other key can be depressed until the first depressed key has been released and returned to its normal position. Alternatively, notched bars 21 as shown may be provided as a keyboard blocking mechanism.

The photo cell 22 may be connected to a radio transmitter i5, Fig. 1, from which the impulse trains defining the characters are transmitted for radiation. The transmitter is operated for only a short interval relative to the character spacing and so may have a very high signal level with respect to the average power consumed. Likewise, the pulses preferabl have a very steep wavefront. The equipment may also be provided with a radio receiver [5 coupled to receiver equipment in casing 59. A visual reproducing arrangement such as a cathode ray screen I6, Fig. 1, may be provided for reproducing the received pulses from a distant station.

Th keys are preferably operated in non-periodic fashion by the operator thus producing a random distribution of the transmitted char acters.. The enemy cannot then jam the transmission by sending pulses of similar character to the character grouping since he cannot know the timing of the operators signals, as there is no fixed timing. As a consequence, the jamming pulses generally will fall between the character signals and will appear on different parts of the screen.

To jam the signals by transmittin energy to cover effectively the whole receiver screen would require a jamming transmission of at least several times the peak signal power. Such a transmitter is so large as to be considered impractical.

Turning to Fig. 3, a better understanding of the transmitter and receiver equipment may be had. In this figure is shown a motor 30, which may be a variable speed motor or any other suitable type, coupled through a gearin mechanism 3| to transmitting drum 20. A scanning control arrangement 33 is operated in timed relation with the transmitting drum 20. This scanning control mechanism may be of a type to be later explained. The output from scanning control 33 operates the horizontal or line and the vertical or frame scanning source 34 from which the scanning waves are applied to cathode ra tube 35 coupled to the output of receiver 35. The output of receiver 36 is preferabl limited to remove the lower level interference in clipper 38 and the clipped energy applied to a control grid 3'! to control the intensity of the cathode ray beam in accordance with the input signals.

Thus, if signals are being received at 36 from some distant station, motor 39 is operated to drive scanning control 33 at substantially the same speed as the transmitter drum, it bein understood that all communicating equipments will have transmitter drums operating at substantially the same speed. By use of known forms of speed control operated by knob I2 the motor at the receiving station may be adjusted to a desired speed. However, in an embodiment of our invention, to be described more fully later, the maintenance of synchronism of the receiver and transmitter is not essential. Line and frame scanning waves are generated at 34 and applied to the deflector plates of 35. As the scanning takes place, the cathode ray beam is altered in intensity b signals impressed on grid 37. The gear assembly 3| may be ordinary reduction gearing for driving the transmitter drum at a lower speed than motor 30.

Transmitter drum 2!! is preferably made of very light material and ma constitute merel an opaque film with the signal elements photographically reproduced thereon as transparent rectangles. Since the transmitter drum is very light in Weight a relatively small motor is required to drive it at the desired high speeds. By using transparent film, different sets of character elements may be readily substituted having differently shaped characters so that should the enemy capture one of the transmitter equipments and begin sending signals to confuse the messages, it is merely necessary to change to a drum having differently shaped characters in order that the true message can be distinguished from the false message from the enemy station.

It is clear that the scanning control mechanism of mechanism 33 may be of any desired type producing impulses for determining the frame and scanning frequencies for the received signal. For example, mechanism 33 might constitute any impulse contacts, one for each revolution of the drum, to provide for the frame synchronizing contact wave and the other having as many contacts as there are lines in the juncture of this instance '1.

If the character is to be reproduced only once, it is necessary that the drive motor be synchronized with the transmitter so that the character will appear properly on the cathode ray screen. In accordance with our invention, however, means may be provided rendering such synchronous relationship unnecessary. An arrangement of this modification of our invention may be better understood by the description made with reference to Figs. 4, 5 and 6.

Turning first to Fig. 4, there are provided two drums ll) and 4| mounted on the same shaft as drum 32 of Fig. 3 and rotated therewith. Drum 40 is provided with a single contact element 42 connected through shaft 43 with a source 44. Cooperating with disc 40 is a brush 45 coupled through a condenser 46 to the grid of a gas discharge tube 41. Tube 41 is connected over relatively high resistor 48 to a source of positive voltage supply and a condenser 49 is connected between resistance 33 andthe plate of tube 41. Because of the large resistance and the positive voltage the voltage of the condenser is built up in accordance with the curve A of Fig. 5. However, upon rotation of disc It to such a position that the conductive segment 42 is in con tact with brush 25 and animpulse is impressed upon the grid of tube El causing the tube to break down and discharge condenser 49. When contact i2 passes brush t5, the charging cycle of the condenser is repeated. Thus, a saw-tooth voltage of curve A, Fig. 5, is produced. This may serve as the normal framing control for the oscillograph. However, in order to reproduce the signal by framing impulses on the upper and lower halves of the screening for the circuit, arrangement is provided. An oscillator 50 producing square waves of the type shown in curve B of Fig. 5 is coupled over condenser 5! to one of th grids of mixing tube 52. Similarly, the saw-tooth output from condenser-resistance circuit 48 i9 is applied over coupling condenser 53 to another grid of tube 52. The tube is preferably relatively high biased by means of the condenser-resistance biasing network 54. Tube 52 becomes conductive in difierent amounts by the application of the square wave B and the saw-tooth wave of curve A to produce a resultant output curve such as shown at C of Fig. 5. It will thus be seen that the cathode ray spot as controlled by the vertical deflecting plates traces a broken line formed by the upper portions U of wave C and a second scanning line represented by the lower portions L of wave C. This will thus produce separate framing impulses for the upper and lower halves of the cathode ray screen. The cathode ray beam is meanwhile controlled in brilliance by the signals applied to the grid 31, Fig. 1, reproducing the character in two positions as shown by Al and A3, Fig. 5. Preferably, the grid is biased so that the beam is completely out off in the absence of received energy.

The second disc 4| is provided with '7 conductive segments 6| to 6'3, inclusive, which are brought successively into contact with brush 55 similarly to the operation of segment 42 with brush 45. Thus, seven separate impulses are impressed on the grid of tube 56 for each rotation. Tube 56 is connected over a resistance 51 to a source of high potential and serves to charge a condenser 58. The time constant of circuit 51-58 is made such as to produce the desired saw-tooth voltage effect for the line scanning. It should be clear that if a different number of lines is desired, a corresponding number of segments should be provided on disc 4|. The sawtooth wave generated in circuit 5i58 is applied to a mixing tube 10 similar to tube 52 and a square wave is also supplied to the mixing tube rroma separate oscillator I l. The resultant output wave is in the form of a serrated saw-tooth shown in curve D of Fig. 5. This resultant wave is applied to the horizontal or line deflecting electrodes of the oscillograph. This serrated wave will thus produce alternate line scanning positions at Al, A2, respectively, Fig. 6.

In operation of the circuit the received impulses are applied to the control grid of the cathode ray oscillograph. During the time while the first line impulses are applied to the grid the cathode ray beam is alternately positioned at Al, A2, A3, A4 to make the four dotted representations of the first line of scanning. Each line of scanning will be broken by the serrated waves so that only one-fourth of the normal line will be present in each character. This will cause a dotted representation of the received character. In order to accomplish switching of the beam during each line of scanning at a sufficiently high rate to provide division of the shortest line impulse, the square waves associated with each of the saw-tooth waves should be at least ten times the frequency of the saw-tooth. For the second line the beam is again switched alternately to th four positions Al, A2, A3, A4 corresponding to the second line of the scanning and so on until the entire character has been reproduced four times on the screen. Should the receiver be out of synchronism with the transmitter then the entire pattern may be shifted on the screen to the positions shown at the right of Fig. 6. In this arrangement Al has become split into four portions, A2 and A4 into two portions each but A3 is produced in its entirety on the screen of the oscillograph. It is thus seen that by breaking the signal up into four parts on the reproduction there will always be at least one of the characters reproduced completely.

It is clear that instead of making four images some other number might be chosen with a corresponding controlof the scanning mechanism to produce the desired number of frames.

It should be clearly understood that many modifications may be made in the system of our invention as disclosed in these particular examples. Instead of a cathode ray cscillograph other known forms of oscillographs may be substituted, if desired. Likewise, the details of the transmitter construction and receiver construction may be varied at will without departing from the scope of our invention.

While we have described above the principles of our invention in connection with specific apparatus, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects of our invention and the accompanying claims.

'W hat is claimed is:

1. A communication system comprising transmitter means for transmitting a series of impulses defining a character during a period of time which is short relative to the time between characters, a series of signal elements related to a selected signal character to be transmitted, said pulses having a sharp wave front and a high ratio of peak to average power, receiving means for receiving said series of pulses, interference minimizing means at said receiver for eliminating all energy below a predetermined level substantially lower than the peak energy level of said signal elements, and reproducing means for reproducing the character represented by said signal elements.

2. A communication system according to claim 1 wherein said transmitter means comprises character designating means provided with different character designations, means for selecting a desired one of said character designations, means operating to position said character designating means into character transmitting position in the order of twenty times in a predetermined cycle, and means operating to transmit said selected character once only during said predetermined cycle.

3. A communication system according to claim 1 wherein said transmitter comprises a rotary drum, said drum being provided with sets of perforations representing said series of signal elementslfor each character to be transmitted, photo-electric means and a cooperating light source cooperating with one another through said perforations, shutter means normally covering said perforations, key mean for selectively operating said shutter means to uncover selected ones of said sets of perforations to permit cooperation of said light source and said photo-electric means, drive means to rotate said drum at a predetermined speed relatively high with respect to the operation time of said keys whereby said character designations are positioned in transmitting position a plurality of times during said cycle, and means to close said shutter means after passage of a relatively small fraction of the time of said cycle.

4. A communication system according to claim 1 wherein said transmitter means comprises character designating means provided with different character designations, means for selecting a desired one of said character designations, means operating to position said character designating means into character transmitting position in the order of twenty times in a predetermined cycle, and means operating to transmit said selected character once only during said predetermined cycle, and said reproducing means comprises visual indicating means for reproducing the selected transmitted character in four separate scanning positions, whereby at least one of said reproduced characters will be complete on said indicator.

5. A communication system of the type using a keyboard mechanism operating in a predetermined time cycle for selecting a particular character represented by a series of signal elements for transmission and a receiver with character indicating and reproducing means, comprising character designating means provided with different character designations, means for positioning said character designating means into character transmitting positions a relatively great number of times during the selecting time cycle, and means responsive to operation of a key of said keyboard mechanism selected at random for transmitting the series impulses representing said selected character for a predetermined relatively small fraction of said predetermined cycle at an energy level high with respect to the average transmitted power, whereby said selected characters are transmitted at a high energy level and at random intervals dependent upon the operation of said keys.

6. A communication system of the type using a keyboard mechanism operating in a predetermined time cycle for selecting a particular character represented by a series of signal elements fOr transmission and a receiver with character indicating and reproducing means, comprising a character designating means provided with different character designations, means for positioning said character designating means into character transmitting positions a relatively great number of times during the selecting time cycle,

means responsive to operation of a selected key of said keyboard mechanism for transmitting the series impulses representing said selected character for a predetermined relatively small fraction of said predetermined cycle at an energy level high with respect to the average transmitted power, whereby said selected characters are transmitted at a high energy level and at random intervals dependent upon the operation of said keys, receiver means for receiving said transmitted series of pulses, visual indicating means for reproducing said character from said received series of pulses, and manual adjustable means for adjusting the operation of said indicating means to synchronize it with the transmitted pulses.

7 A communication system according to claim 6 further comprising means for eliminating received energy below a predetermined level substantially lower than said transmitting energy level to minimize interference effects.

8. A communication system according to claim 6 wherein said relatively small fraction of said cycle includes a period sufiicient to transmit said character once only, said receiver and visual indicating means further comprising means for reproducing said character a plurality of times at different positions, whereby at least one of said reproductions will be complete.

9. The method of communication comprising transmitting a series of impulses related to a selected character during a period of time which is short relative to the time between characters, shaping said impulses to provide a sharp wavefront and a high ratio of peak to average power, receiving said transmitted pulse series, and visually reproducing said selected character from said received pulse series, whereb said reproduced characters will have a greater visual brilliance than interference energy because of said high energy level.

10. The method of communication comprising transmitting a series of impulses related to a selected character during a period of time which is short relative to the time between characters, shaping said impulses to provide a sharp wavefront and a high ratio of peak to average power, receiving said transmitted pulse series, clipping said received pulse series to eliminate all energy below a predetermined level substantially lower than said peak energy level to reduce interference, and reproducing said received clipped pulse series.

11. The method of communication comprising transmitting several series of impulses related to a selected character during a period of time which is short relative to the time between characters, shaping said impulses to provide a sharp wavefront and a high ratio of peak to average power, receiving said transmitted pulse series, and visually reproducing said selected character from said received pulse series in several positions, whereby said reproduced characters will have a greater visual brilliance than interference energy because of said high energy level and at least one unitary reproduction despite lack of synchronism in transmission and reception.

EDMOND M. DELORAINE. HENRI G. BUSIGNIES. LOUIS A. DE ROSA. 

